Two-stroke internal combustion engine



March 26, 1968 B. HOOPER TWO'STROKE INTERNAL COMBUSTION ENGINE 5 Sheets-Sheetl Filed Sept. 27, 1966 aemunkp Hoopfi e kl An e i- March 26 1968 s. HOOPER 3,374,775

Two-STROKE INTERNAL COMBUSTION ENGINE Filed Sept. 27, 1966 5 Sheets-Sheet 2 March 26, 1968 B. HOOPER 3,374,776

TWO-STROKE INTERNAL COMBUSTION ENGINE Filed Sept. 27, 1966 5 Sheets-Sheet 5 March 26, 1968 HOOPER 3,374,776

TWO-STROKE INTERNAL COMBUSTION ENGINE Filed Sept. 2'7, 1966 v 5Sheets-Sheet 4 Km KM March 26, 1968 B. HOOPER 3,374,776

TWO-STROKE INTERNAL COMBUSTION ENGINE Filed Sept. 27, 1966 5 Sheets-Sheet 5 Agar-r United States Patent 3,374,776 TWO-STROKE INTERNAL COMBUSTION ENGINE Bernard Hooper, Wordsley, Stourbridge, England, assignor to The Villiers Engineering Company Limited, Wolverhampton, England, a British company Filed Sept. 27, 1966, Ser. No. 582,341 Claims priority, application Great Britain, Oct. 8, 1965,

42,881/ 65 V 12 Claims. (Cl. 12373) This invention relates to two-stroke internal combustion engines of the kind employing crank case compression, i.e. wherein for the or each cylinder, a charge of air, or air and fuel vapour, is compressed in a crank chamber of a crank case by the piston approaching bottom dead centre position and which then passes through transfer passage means to emerge at the upper end thereof in the cylinder above the piston. In such engines it has previously been proposed to pass the charge into the lower,

i.e. crank chamber, end of main transfer passage means formed in the cylinder and crank case through auxiliary transfer passage means formed in the main journal or journals of the crank shaft and in the complementary journal bearing or bearings which are of the plain type. Engines having the above features will hereinafter be referred to as being of the kind described.

The term passage means used herein is intended to include one or more discrete passages for the flow of gas. The terms upper and lower and up and down are used herein to define positions and directions in the engines when the latter are in positions with the cylinders arranged above the crank shaft.

It is an object of this invention to provide a simplified construction for an engine of the kind described which allows the engine to be manufactured at low cost but which provides satisfactory cooling and lubrication of the main crank shaft journal hearing or bearings.

According to the invention we provide an engine of the kind described wherein, for the each cylinder there are, during the major portion of the time during which transfer of the charge from the crank chamber to the cylinder occurs, two paths for the charge from the chamher into the main transfer passage means apart from the normal working clearance between the piston and the cylinder, the first of said paths being through the auxiliary transfer passage means and the second of said paths comprising one or more small clearances between a part or parts of the crank shaft and/or piston and a stationary part or parts of the engine, the relation between the restrictions offered to gas flow by the two paths being such that the major portion of the charge flows through the auxiliary transfer passage means during said transfer.

By virtue of the construction embodying the invention, it is not necessary to provide complete sealing of the main transfer passage means during transfer so long as the restriction offered to gas flow through the small clearances provide is considerably greater than the restriction offered by the auxiliary transfer passage means so that the major proportion of the charge passes through the auxiliary transfer passage means.

Four embodiments of the invention will now be described in detail by way of example with reference to the accompanying drawings in which:

FIGURE 1 is a vertical section through an engine constitutin g a first embodiment of the invention;

FIGURE 2 is a vertical section on the line 11-11 of FIGURE 1; 7

FIGURE 3A is a section similar to half FIGURE 2 of a second embodiment of the invention;

FIGURE 3B is a section similar to FIGURE 3A showing a third embodiment of the invention;

FIGURE 4 is a section similar to FIGURE 2 of a fourth embodiment of the invention; and

FIGURE 5 is a diagram indicating the optimum position for a port in a crank shaft journal.

Referring now to FIGURES 1 and 2, the engine there shown comprises a cylinder block or barrel 10 which is of one piece construction and which at its lower end has a spigot 11 Which is received in a bore 12 provided in a split crank case 13. The parts of the crank case 13 are held together in a conventional manner by means of bolts 14. Slidable within a cylinder 15 in the block 10 is a piston 16 connected by means of a connecting rod 17 to a crank shaft indicated generally at 18. Referring particularly to FIGURE 2, the crank shaft has two main journals 19 which run in plain journal bearings 20 in the crank case. The crank shaft is preferably of one piece cast construction and is provided with a crank pin 21 which is embraced by the big end bearing 22 of the connecting rod 17. The upper end of the connecting rod has a small end bearing 23 in which is engaged a gudgeon pin 24 received in the piston 16.

The cylinder block 10 is provided with an inlet spigot 25 and an outlet spigot 26 to which may be .bolted an exhaust pipe 27. The cylinder also is provided with a sparking plug 28.

The engine is of the crank case compression ty e. That is to say that a charge of fuel and air flows in along the inlet spigot 25, passes .to a crank case chamber 29 within the crank case, is compressed as the piston 16 descends to adjacent its bottom dead centre position and then passes into the cylinder above the piston to be compressed and exploded by the sparking plug 28.

The charge passes into the crank chamber 29 and from the chamber 29 into the cylinder 15 by means of transfer passage means which will now be described. These means comprise firstly, main transfer passage means which are formed in the cylinder block 10 and in the crank case 13. The transfer passage means comprises, in the wall of the cylinder, two pairs of channels 30, each channel being open along its whole length to the cylinder bore. Each pair of channels 30 communicates, at the lower ends 31 of the channels, with the upper end 32 of a passage 33 formed Within the thickness of the Wall of the crank case. Each passage 33 is isolated from the crank chamber by means of a wall 34 and the upper end of this wall is formed into a cylindrical spigot 35 of a diameter such that it fits within the skirt 36 of the piston 16 with a small radial clearance of the order of 0.02" indicated at 37.

The crank shaft is provided with two webs 38 and formed within the crank shaft in the journals 19, the webs 38 and the crank pin 21 is auxiliary transfer passage means. These transfer passage means include a port 39 in each of the journals 19, a port 40 in each of the webs 38, a passage 41 between each adjacent port 39 and 40 and a lubricating passage 42 passing through the crank pin and placing in communication the passages 41. A port 43 is provided in the lubricating passage 42 and is closed at its outer end by the big end bearing 22, the latter being provided with a slot 22a. The ports 39 in the journals 19 come into alignment with ports 44 in the bearings 20 at predetermined intervals to allow charge to flow from the crank chamber 29 through the ports 40, the passages 41 and the ports 39 into the passages 33 and then into the channels 30 and into the cylinder 15.

The operation of the engine follows conventional practice. As the piston descends after firing, it first uncovers the passage 45 in the exhaust spigot and allows exhaust to escape thus decreasing the pressure in the cylinder. The upper ends 46 of the channels 30 are then uncovered by the piston and allow charge to flow'from the crank chamber 29 in the manner described above into the cylin- 3 I der 15. As the piston rises, the various passages will be shut off in turn and the charge will be compressed and fired by the plug 28. The raising of the piston creates a depression in the crank chamber 29 and adjacent. top dead centre the piston rises above the passage 47 in the inlet spigot 25 and allows a charge of air and fuelto flow into the crank chamber 29. As the piston descends it will compress the charge which has been introduced into the crank chamber 29 and this compression will continue until the upper ends 46 of the channels 30 are uncovered thus allowing the charge to flow into the cylinder as described above.

It will be noted that there are two paths for the charge to flow from the crank chamber 29 into the passages 33. The charge can either flow through the auxiliary transfer passage means comprising the ports 40, the passages 41 and the ports 39 and 44 or the charge can flow through the small clearance 37. However, the relation between the restrictions to gas flow of the clearance 37 and the auxiliary transfer passage means is such that the major portion of the charge flows through the passages 41. By this means, the main journal bearings are lubricated because the fuel contains lubricating oil and are also adequately cooled. Similarly the big end bearing is lubricated and cooled through the passage 42 and the port 43. It follows that although during the transfer of the charge some will flow through the clearance 37, by proper design suflicient of the charge can be caused to flow through the journal hearings to keep them adequately cooled and lubricated. They will be lubricated because a certain amount of the oil will remain in the passages 41 and 42 and during rotation of the crank shaft will be flung out against the parts of the bearings and 22 to lubricate them. Moreover the path of travel of the charge through the passages keeps the bearings adequately cool. The slot 22a will also assist with lubrication of the big-end bearing.

Turning now to the embodiments shown in FIGURES 3A and 3B these are in many respects similar to that shown in FIGURES l and 2 and similar parts are indicated by the same reference numerals however, in these constructions, the wall 34 is dispensed with and the channels in the cylinder block 10 communicate at their lower ends with channels 48 formed in the wall 49 of the crank case. These channels are open throughout their whole lengths to the crank chamber 29.

The spigot is formed at its lower end with a flange 50 and the channels 48 are, during transfer, sealed except for small clearances by means of the Webs 38 of the crank shaft. Thus in FIGURE 3A there is a small clearance 51 between the flange 50 and the peripheral surface 52 of each crank web 38. There is also a small clearance 53 between the open side of each channel 48 and the face 54 of each crank web which is directed towards the open end of the channel and -is perpendicular to the rotary axis 55 of the crank shaft. There is also the clearance 37 as in the construction of FIGURES l and 2.

In FIGURES 3B the face 54a is spaced a comparatively large distance from the crank case wall but the latter and the web 38 are made so that around the whole of its peripheral surface 52 there is a small clearance indicated at 51 between the surface 52- and the flange 50 1:lind at 51a between the surface 52 and the crank case wa In FIGURES 3A and 3B the clearances 37, 51 and 51a may be 0.02" and the clearance 53 may be 0.03.

The operation of the embodiments of FIGURES 3A and 3B is identical to that of FIGURES l and 2 except that the charge flows through the channels 48 rather than through the passages 33, the channels being substantially sealed except for the small clearances 51 and 53 or 51 and 51a. In these constructions it is apparent that the engine must be designed so that the total restriction to flow provided by the small clearances 37, 51 and 53 or 5111 is such, when compared with the auxiliary transfer passage means through the crank shaft, that a suflicient quantity of the charge goes through the auxiliary transfer passage means to lubricate and cool the main bearings and the big end bearing.

Referring now to FIGURE 4, this is substantially similar to the arrangements shown in FIGURES 3A and 3B except that the cylinder block 10 contains a liner 55 within which the piston 16 Works. The spigot 35 of FIGURES 3A and 3B is also dispensed with and at the bottom of the liner 55 there is a flange 56 forming part of the crank case and which takes the place of the flange 50 on the spigot 35. Thus during transfer of the charge from the crank chamber 29 to the cylinder 15, the charge flows into the channels 48nd from the channels into passages 57 between the liner and the block and thus into the cylinder. The channels 48 are substantially sealed except for the small clearances 53 as in FIGURE 3A and a further small clearance 58 between the flange 56 and ance between the piston and the cylinder, two paths for the charge into the main transfer passage means comprising the channels 30 and passages 33 in FIGURES 1 and 2, the channels 30 and 48 in FIGURES 3A and 3B and the channels 48 and passages 57 in FIGURE 4. One of these paths is through the auxiliary transfer passage means, i.e. through the passages 41 in the crank shaft as shoWn'in FIGURE 2. The other path is through small clearances. In FIGURE 2 the other path is constituted solely by the small clearance 37; in FIGURE 3A by the small clearances 37, 51 and 53, in FIGURE 3B by the small clearances 37, 51 and 51a, and in FIGURE 4 thereby the small clearances 53 and 58. The clearances are so dimensioned as to direct most of the flow through the crank shaft passages 41. The total area of the small clearances in each embodiment considered perpendicular to.

the direction of flow of gas therethrough is preferably not more than 25% of the areas of the upper ends of the transfer passages, e.g. 46, where these intersect the cylinder, also measured perpendicular to the direction of gas flow therethrough.

The major components can all be made by high production casting processes using pressure or gravity dies or shell moulds which makes for cheap construction. Moreover, eflicient lubrication of the main crank shaft bearings and the big end bearing or bearings is obtained with less lubricant than is used at the moment in engines employing main bearings of the plain type.

Referring now to FIGURE 5, this shows the optimum position for the ports 39 in the crank shaft journals 19 of a single cylinder engine. The curve 59 is a polar diagram, on the base line 59a, of the load on the crank shaft journal bearing surface which is made up of the inertia loads and the gas loads. The curve is drawn for a condition when the engine is operating at maximum speed and power. It will be seen that there is a portion of the surface at which the load is a minimum andthe port 39 is advantageously located so that it opens, into this part of the journal surface. It is to be noted that the optimum position for the centre line 60 of the port lies between a line 61 and a line 62 which are respectively 60 and from the centre line 63 of the crank pin considered in the direction of the arrow A which is opposite to 'the normal direction of rotation of the shaft which is indicated by the arrow, B. For a multicylinder engine similar diagrams could be drawn and the ports located appropriately. Various modifications may be while remaining within remaining within the scope of the invention. Thus it isunnecessary for a spigot 35 to be completely cylindrical. -It could be replaced by two parts spigots which are overlapped by the skirt 36, the part spigots being opposite to the passages 33 so as to provide the necessary small clearances. Alternatively, part spigots could be used which were located outside the piston skirt and the latter could overlap the spigot parts with small clearance. A separate cylinder head could be used. Any conventional means such as reed valves, rotary valves and poppet valves may be used to control the inlet and exhaust periods The invention is also applicable to single cylinder engines having overhung crank shafts and, there would only be a single passage through the crank shaft. The invention can also be applied to multicylinder engines by placing together two or more single cylinder engines in which some parts are common.

If desired each channel or passage in the crank case may communicate either with a single passage or channel in the cylinder or with three or more such passages or channels.

What I claim then is:

1. A two-stroke internal combustion engine employing crank case compression and including a cylinder, a piston reciprocable in the cylinder, a crank case defining a crank chamber, a crank shaft rotatably mounted by main journal means in the crank case and connected to the piston to form an assembly, main transfer passage means between the crank chamber and the cylinder for transferring the charge therebetween and auxiliary transfer passage means in said main journal means to pass the charge from the crank chamber to the main transfer passage means, and wherein during the major portions of the time during which transfer of the charge from the crank chamber to the cylinder occurs, two paths for the charge from the chamber into the main transfer passage means apart from the normal working clearance be tween the piston and the cylinder, the first of said paths being through the auxiliary transfer passage means and the second of said paths comprising a small clearance between the crank shaft and piston assembly and stationary abutment means of the engine, the relation between the restrictions offered to gas flow by the two paths being such that the major part of the charge flows through the auxiliary passage means during transfer.

2. An engine according to claim 1 wherein the main transfer passage means includes at least one channel formed in the wall of the cylinder and open along its whole length to the cylinder bore and wherein said second path comprises a small clearance between the skirt of the piston and a fixed spigot forming part of said abutment means and overlapped by the skirt during said transfer.

3. An engine according to claim 2 wherein the main transfer passage means includes a number of channels in the crank case wall, and at least one channel in the crank case wall and open along its whole length to the crank chamber and, during said transfer, being cut off from the crank chamber except for small clearances between the crank case wall and the spigot on the one hand and said crank shaft and piston assembly on the other hand and being open at its lower end to the auxiliary transfer passage means, each channel in the cylinder Wall communicating at its lower end with the upper end of a channel in the crank case Wall.

4. An engine according to claim 3 wherein the crank shaft and piston assembly includes web means having face means perpendicular to the axis of the crank shaft and being spaced by said small clearance from the crank case wall and having outer peripheral surface means spaced by said small clearance from the spigot.

5. An engine according to claim 3 wherein the crank shaft and piston assembly includes web means having outer peripheral surface means spaced by said small clearance from the crank case wall and from the spigot.

6. An engine according to claim 2 wherein the main transfer passage means includes a number of passages formed in the thickness of the crank case wall, each channel in the cylinder wall communicating at its lower end with the upper end of a passage in the crank case wall, each of the passages being permanently isolated from the crank chamber by a wall and having its lower end open, during said transfer, to the auxiliary transfer passage means.

7. An engine according to claim 1 wherein the main transfer passage means includes at least one channel formed in the crank case wall and open along its whole length to the crank chamber, the channel, during said transfer, being cut off from the crank chamber except for small clearances between the crank case wall and a member at the bottom of the cylinder wall on the one hand and parts of the crank shaft and piston assembly on the other hand and being open at its lower end to the auxiliary transfer passage means.

8. An engine according to claim 7 wherein the main transfer passage means includes a number of passages formed between the cylinder block and a liner therefor, each passage communicating at its lower end with the upper end of a channel.

9. An engine according to claim 1 wherein the auxiliary transfer passage means in the crank shaft journal or journals lead into a lubrication passage which opens to a big-end bearing.

10. An engine according to claim 1 wherein the auxiliary transfer passage means includes in each journal through which the charge is transferred and wherein the port is located so that it is within the region of minimum radial load on the journal bearing surface when the engine is operating at maximum rated power and speed.

11. A single cylinder engine according to claim 10 wherein said port is located at a position, when viewed along the axis of the crank shaft, so that its centre is between and from the centre line of the crank pin when considered in the directing opposite to the normal direction of rotation of the crank shaft.

12. An engine according to claim 1, wherein for the cylinder the total area of the small clearance considered perpendicular to the direction of gas flow therethrough is not more than 25% of the area of the main transfer passage means where these interesect the cylinder, said latter area also being measured perpendicular to the direction of gas flow therethrough.

References Cited UNITED STATES PATENTS 2,959,164 11/1960 Way et a1. 12373 FOREIGN PATENTS 270,803 5/1927 Great Britain. 758,654 10/1956 Great Britain.

WENDELL E. BURNS, Primary Examiner. 

1. A TWO-STROKE INTERNAL COMBUSTION ENGINE EMPLOYEDING CRANK CASE COMPRESSION AND INCLUDING A CYLINDER, A PISTON RECIPROCABLE IN THE CYLINDER, A CRANK CASE DEFINING A CRANK CHAMBER, A CRANK SHAFT ROTATABLY MOUNTED BY MAIN JOURNAL MEANS IN THE CRANK CASE AND CONNECTED TO THE PISTON TO FORM AN ASSEMBLY, MAIN TRANSFER PASSAGE MEANS BETWEEN THE CRANK CHAMBER AND THE CYLINDER FOR TRANSFERRING THE CHARGE THEREBETWEEN AND AUXILIARY TRANSFER PASSAGE MEANS IN SAID MAIN JOURNAL MEANS TO PASS THE CHARGE FROM THE CRANK CHAMBER TO THE MAIN TRANSFER PASSAGE MEANS, AND WHEREIN DURING THE MAJOR PORTIONS OF THE TIME DURING WHICH TRANSFER OF THE CHARGE FROM THE CRANK CHAMBER TO THE CYLINDER OCCURS, TWO PATHS FOR THE CHARGE FROM THE CHAMBER INTO THE MAIN TRANSFER PASSAGE MEANS APART FROM THE NORMAL WORKING CLEARANCE BETWEEN THE PISTON AND THE CYLINDER, THE FIRST OF SAID PATHS BEING THROUGH THE AUXILIARY TRANSFER PASSAGE MEANS AND THE SECOND OF SAID PATHS COMPRISING A SMALL CLEARANCE BETWEEN THE CRANK SHAFT AND PISTON ASSEMBLY AND STATIONARY ABUTMENT MEANS OF THE ENGINE, THE RELATION BETWEEN THE RESTRICTIONS OFFERED TO GAS FLOW BY THE TWO PATHS BEING SUCH THAT THE MAJOR PART OF THE CHARGE FLOWS THROUGH THE AUXILIARY PASSAGE MEANS DURING TRANSFER. 